Conventional banknote acceptors authenticate a banknote under test by checking its physical properties against stored reference data and signalling the authenticity of the banknote depending on the outcome of the comparison. The banknote under test may be scanned optically to produce digital image data corresponding to one or both sides of the banknote. The image data is compared with stored reference data corresponding to acceptable banknotes to authenticate the banknote under test. Also, the denomination of the banknote can be determined so that credit corresponding to the monetary value of the banknote can be allocated. Banknote acceptors have been used hitherto in gaming and vending machines to provide credit for gaming or making purchases.
A problem with conventional banknote acceptors is that the user may dispute the outcome of the authentication process and may dispute the monetary value of the credit allocated to the banknote under test.
For example, the user may contend that a higher value banknote was presented to the banknote acceptor than the monetary credit allocated. Such a dispute can be time consuming to resolve and may require a machine operator to open the machine in which the banknote acceptor is installed to retrieve the banknote and physically examine it.